Check it: http://www.filife.com/guides/all-about-401ks

I'm the sort of kid who eats their peas first, so I advise paying your taxes now and letting your savings marinate in a (f)Roth(y) 401k. But if you like to mix your flavors contribute to both a 401k and a Roth 401k. You'll have to pay taxes when you eventually draw from the regular 401k, but maybe it'll be at a lower rate in the future. ...maybe.

It all depends on your personal tax situation. A lot of people are in a low income tax bracket while they are young (right out of college or high school) and then usually move into a higher tax bracket towards the end of their careers and in retirement. Because regular 401-k money is taxed when you withdraw it, you would then end up paying more in taxes using a traditional 401-k retirement plan rather than the Roth option in most scenarios. Roth 401-k plans are funded with money that is already been taxed, grows tax free, and capital gains and distributions are then NOT taxed in retirement. There is a distinct tax advantage to maxing out your contributions to a Roth 401-k plan first, and then investing in a traditional plan after that.

If you think you will be in the same tax bracket in retirement as you are now and you have at least 10 years before you are going to draw on the money a Roth is definitely the best way to go. There are two things that make a Roth especially appealing right now. The first is that tax rates will probably go up so you will pay even more on a traditional IRA or 401k in future. Secondly, stock market values are low so you can to buy more with your after tax dollars. Once your money is in a Roth you will not have to pay tax on the increase in value when the stock market rebounds. This should be a significant consideration.